245 lines
8.2 KiB
C++
245 lines
8.2 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_dom_DOMString_h
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#define mozilla_dom_DOMString_h
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#include "nsStringGlue.h"
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#include "nsStringBuffer.h"
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#include "mozilla/Assertions.h"
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#include "mozilla/Attributes.h"
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#include "mozilla/Maybe.h"
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#include "nsDOMString.h"
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#include "nsIAtom.h"
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namespace mozilla {
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namespace dom {
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/**
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* A class for representing string return values. This can be either passed to
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* callees that have an nsString or nsAString out param or passed to a callee
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* that actually knows about this class and can work with it. Such a callee may
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* call SetStringBuffer or SetEphemeralStringBuffer or SetOwnedString or
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* SetOwnedAtom on this object. It's only OK to call
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* SetStringBuffer/SetOwnedString/SetOwnedAtom if the caller of the method in
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* question plans to keep holding a strong ref to the stringbuffer involved,
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* whether it's a raw nsStringBuffer, or stored inside the string or atom being
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* passed. In the string/atom cases that means the caller must own the string
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* or atom, and not mutate it (in the string case) for the lifetime of the
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* DOMString.
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*
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* The proper way to store a value in this class is to either to do nothing
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* (which leaves this as an empty string), to call
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* SetStringBuffer/SetEphemeralStringBuffer with a non-null stringbuffer, to
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* call SetOwnedString, to call SetOwnedAtom, to call SetNull(), or to call
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* AsAString() and set the value in the resulting nsString. These options are
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* mutually exclusive! Don't do more than one of them.
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*
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* The proper way to extract a value is to check IsNull(). If not null, then
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* check HasStringBuffer(). If that's true, check for a zero length, and if the
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* length is nonzero call StringBuffer(). If the length is zero this is the
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* empty string. If HasStringBuffer() returns false, call AsAString() and get
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* the value from that.
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*/
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class MOZ_STACK_CLASS DOMString {
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public:
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DOMString()
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: mStringBuffer(nullptr)
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, mLength(0)
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, mIsNull(false)
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, mStringBufferOwned(false)
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{}
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~DOMString()
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{
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MOZ_ASSERT(!mString || !mStringBuffer,
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"Shouldn't have both present!");
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if (mStringBufferOwned) {
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MOZ_ASSERT(mStringBuffer);
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mStringBuffer->Release();
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}
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}
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operator nsString&()
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{
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return AsAString();
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}
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// It doesn't make any sense to convert a DOMString to a const nsString or
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// nsAString reference; this class is meant for outparams only.
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operator const nsString&() = delete;
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operator const nsAString&() = delete;
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nsString& AsAString()
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{
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MOZ_ASSERT(!mStringBuffer, "We already have a stringbuffer?");
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MOZ_ASSERT(!mIsNull, "We're already set as null");
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if (!mString) {
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mString.emplace();
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}
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return *mString;
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}
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bool HasStringBuffer() const
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{
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MOZ_ASSERT(!mString || !mStringBuffer,
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"Shouldn't have both present!");
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MOZ_ASSERT(!mIsNull, "Caller should have checked IsNull() first");
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return !mString;
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}
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// Get the stringbuffer. This can only be called if HasStringBuffer()
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// returned true and StringBufferLength() is nonzero. If that's true, it will
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// never return null. Note that constructing a string from this
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// nsStringBuffer with length given by StringBufferLength() might give you
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// something that is not null-terminated.
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nsStringBuffer* StringBuffer() const
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{
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MOZ_ASSERT(!mIsNull, "Caller should have checked IsNull() first");
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MOZ_ASSERT(HasStringBuffer(),
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"Don't ask for the stringbuffer if we don't have it");
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MOZ_ASSERT(StringBufferLength() != 0, "Why are you asking for this?");
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MOZ_ASSERT(mStringBuffer,
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"If our length is nonzero, we better have a stringbuffer.");
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return mStringBuffer;
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}
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// Get the length of the stringbuffer. Can only be called if
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// HasStringBuffer().
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uint32_t StringBufferLength() const
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{
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MOZ_ASSERT(HasStringBuffer(), "Don't call this if there is no stringbuffer");
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return mLength;
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}
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// Tell the DOMString to relinquish ownership of its nsStringBuffer to the
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// caller. Can only be called if HasStringBuffer().
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void RelinquishBufferOwnership()
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{
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MOZ_ASSERT(HasStringBuffer(), "Don't call this if there is no stringbuffer");
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if (mStringBufferOwned) {
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// Just hand that ref over.
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mStringBufferOwned = false;
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} else {
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// Caller should end up holding a ref.
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mStringBuffer->AddRef();
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}
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}
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// Initialize the DOMString to a (nsStringBuffer, length) pair. The length
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// does NOT have to be the full length of the (null-terminated) string in the
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// nsStringBuffer.
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void SetStringBuffer(nsStringBuffer* aStringBuffer, uint32_t aLength)
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{
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MOZ_ASSERT(mString.isNothing(), "We already have a string?");
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MOZ_ASSERT(!mIsNull, "We're already set as null");
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MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
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MOZ_ASSERT(aStringBuffer, "Why are we getting null?");
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mStringBuffer = aStringBuffer;
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mLength = aLength;
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}
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// Like SetStringBuffer, but holds a reference to the nsStringBuffer.
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void SetEphemeralStringBuffer(nsStringBuffer* aStringBuffer, uint32_t aLength)
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{
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// We rely on SetStringBuffer to ensure our state invariants.
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SetStringBuffer(aStringBuffer, aLength);
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aStringBuffer->AddRef();
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mStringBufferOwned = true;
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}
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void SetOwnedString(const nsAString& aString)
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{
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MOZ_ASSERT(mString.isNothing(), "We already have a string?");
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MOZ_ASSERT(!mIsNull, "We're already set as null");
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MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
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nsStringBuffer* buf = nsStringBuffer::FromString(aString);
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if (buf) {
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SetStringBuffer(buf, aString.Length());
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} else if (aString.IsVoid()) {
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SetNull();
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} else if (!aString.IsEmpty()) {
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AsAString() = aString;
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}
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}
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enum NullHandling
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{
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eTreatNullAsNull,
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eTreatNullAsEmpty,
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eNullNotExpected
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};
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void SetOwnedAtom(nsIAtom* aAtom, NullHandling aNullHandling)
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{
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MOZ_ASSERT(mString.isNothing(), "We already have a string?");
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MOZ_ASSERT(!mIsNull, "We're already set as null");
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MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
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MOZ_ASSERT(aAtom || aNullHandling != eNullNotExpected);
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if (aNullHandling == eNullNotExpected || aAtom) {
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SetStringBuffer(aAtom->GetStringBuffer(), aAtom->GetLength());
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} else if (aNullHandling == eTreatNullAsNull) {
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SetNull();
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}
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}
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void SetNull()
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{
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MOZ_ASSERT(!mStringBuffer, "Should have no stringbuffer if null");
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MOZ_ASSERT(mString.isNothing(), "Should have no string if null");
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mIsNull = true;
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}
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bool IsNull() const
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{
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MOZ_ASSERT(!mStringBuffer || mString.isNothing(),
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"How could we have a stringbuffer and a nonempty string?");
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return mIsNull || (mString && mString->IsVoid());
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}
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void ToString(nsAString& aString)
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{
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if (IsNull()) {
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SetDOMStringToNull(aString);
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} else if (HasStringBuffer()) {
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if (StringBufferLength() == 0) {
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aString.Truncate();
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} else {
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// Don't share the nsStringBuffer with aString if the result would not
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// be null-terminated.
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nsStringBuffer* buf = StringBuffer();
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uint32_t len = StringBufferLength();
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auto chars = static_cast<char16_t*>(buf->Data());
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if (chars[len] == '\0') {
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// Safe to share the buffer.
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buf->ToString(len, aString);
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} else {
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// We need to copy, unfortunately.
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aString.Assign(chars, len);
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}
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}
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} else {
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aString = AsAString();
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}
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}
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private:
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// We need to be able to act like a string as needed
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Maybe<nsAutoString> mString;
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// For callees that know we exist, we can be a stringbuffer/length/null-flag
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// triple.
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nsStringBuffer* MOZ_UNSAFE_REF("The ways in which this can be safe are "
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"documented above and enforced through "
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"assertions") mStringBuffer;
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uint32_t mLength;
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bool mIsNull;
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bool mStringBufferOwned;
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};
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} // namespace dom
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} // namespace mozilla
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#endif // mozilla_dom_DOMString_h
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